Bulk liquid products such as liquefied industrial gases, are transported to consumers over the road by bulk liquid transport vehicles such as tractor-trailer combinations. The trailer is filled by connecting the trailer to a storage tank or other source of bulk liquid with the use of a fill line and then opening a fill valve to fill the trailer with the bulk liquid.
Typically, quality assurance tests are conducted to ensure that the bulk liquid to be distributed to customers by the trailer meets certain purity and compositional specifications. This is a two step process that begins before the filling process begins by sampling vapor from the trailer with the use of a gas analyzer to make certain that the gas meets overall purity specifications. After the filling process has been completed, vapor from within the trailer is again sampled and more extensive tests are performed that involve quantifying the composition of the vapor.
As can be appreciated, if the fill line is not connected to the trailer when the fill valve is opened from the storage tank, the liquid will simply flow into the bay area in which the filling operation is conducted. This can be particularly dangerous in case of liquid oxygen or other types of bulk liquids to be transported, for example, hydrocarbon containing liquids.
In addition, a further problem exists with respect to the use of the gas analyzer. For most gas analyzers, there must be sufficient vapor pressure within the trailer prior to the commencement of the filling operation in order for the gas analyzer to properly function. If the vapor pressure is too low the gas analyzer will not function and in such case, the quality assurance test fails. If there exists sufficient liquid within the trailer, the driver can build pressure within the trailer and attempt to conduct the test a second time. If there is not sufficient liquid within the trailer, specialized plant personnel are then called to pre-pressurize the trailer. This results in unacceptably long and expansive delays in concluding the filling operation.
In the prior art, it has been known to somewhat automate the filling process with the use of pressure switches and transducers to ascertain whether sufficient pressure exists within the fill line to infer that the fill line is in fact connected to the trailer or there exists a break in the fill line. The pressure that is measured arises from residual liquid within the trailer prior to the filling operation. The problem remains, however, even if the fill line is at a suitable pressure, there might not be sufficient pressure within the trailer for the gas analyzer to properly function.
As will be discussed, the present invention provides an automated system for conducting a filling operation in which not only is it assured that the fill line is connected between the source of the bulk liquid and the trailer but that there also exists sufficient vapor pressure within the trailer for the gas analyzer to properly function.